Various exhaust gas treatment units, for example, catalytic converter devices or particle filters, are used in such exhaust systems to reduce the emission of pollutants. Catalytic converter devices must have, in particular, a temperature in the range of at least 200° C. to 250° C. for an efficient conversion of the pollutants being transported in the combustion waste gases. Such a high temperature further reliably guarantees the evaporation of a urea solution injected as a reactant into the exhaust gas stream for a selective catalytic reduction. Since the catalytic converter devices, through or around which no combustion flow gases have flowed before, will have a temperature markedly below such an activation temperature, above all at the beginning of the operation of an internal combustion engine, the exhaust gas stream is emitted essentially untreated and with a high percentage of pollutants until the necessary temperatures are reached in the area of the catalytic converter devices. Increasingly strict legal requirements shorten the duration during which such a high percentage of pollutants is allowed.